Optical technologies have been widely employed in pointer systems for cursor or frame control on computer displays. For example, optical mice and optical trackballs are the most popular pointer devices currently. The optical pointer device works by detecting a specified image, tracking the displacement of the specified image, and then generating responsive signals to the computer to conduct the movement of a cursor on the display.
Referring to FIG. 1, a working principle of a conventional optical mouse is schematically shown. The optical mouse principally comprises a housing 1, a light source 10 such as a light-emitting diode (LED) and an image receiver 11. The optical mouse is required to work on a plane 12 of a certain material. The plane 12 has to be made of a light-reflective material so that the light emitted by the light source 10 can be reflected by the plane 12 as an image signal and then received by the image receiver. The LED light source and image receiver is now commercially available as an image sensor module.
When the optical mouse rests on the plane 12, the image data of the plane 12 is recorded by the image sensor at a predetermined time interval, wherein the light source generator 10 continuously emits light, and the light reflected by the plane 12 is received by the image receiver 11. With the detected movement of the optical mouse from a first position to a second position on the plane 12 in response to the manipulation of the user, the image data of the plane 12 obtained by the image sensor change. By comparing the recorded image data at the first and the second positions, the displacement data of the optical mouse from the first position to the second position can be realized. The displacement data including the movement direction and distance are then provided for the computer to correspondingly control the movement direction and distance of the cursor or the like.
The conventional optical mouse, unfortunately, has inherent requirements. That is, a plane having at least certain area enough for movably operating the optical mouse is required, and the plane is required to be smooth and flat enough for the optical mouse to smoothly move thereon and for the light emitted by the light source to be reflected and received as expected. In other words, the application of the optical mouse is restricted.
Referring to FIG. 2, another conventional optical pointer device so-called as an optical trackball is shown. The optical trackball principally comprises a housing 2, a trackball element 21 and a displacement detector (not shown) inside the housing 2 to work with the trackball element 21. The image sensor module used in the device of FIG. 1 can be used herein as the displacement detector. When a user rotates the trackball element 21 to result in the movement of the trackball surface relative to the displacement detector, the image data of the trackball surface detected by the displacement detector change so as to obtain the displacement data of the trackball element 21 accordingly. Based on the displacement data, the corresponding movement direction and distance of a cursor or the like on the display is conducted.
In general, a user manipulates the optical trackball by rotating the trackball element 21 with his thumb of the hand holding the housing 2 (or the index finger when the trackball element 21 is mounted on the upper surface of the housing 21. The rotation of a ball element with a single finger, however, is hard to be precisely controlled.